Unable to understand the concept behind DP tree

#1

I am unable to understand the concept that why it is important to use dp in trees.
In the video only application is given via question.

#2

DP involves solving a problem using solutions to subproblems, and proceeding from the bottom up. When you do “DP over trees”, the original problem involves the whole tree, and the subproblems are subtrees; when you know the answer for the subtrees, you can compute the answer for the whole tree. So this is just like basic dp.

I would recommend you to read this blog https://codeforces.com/blog/entry/20935
and this link for video explanation https://www.youtube.com/playlist?list=PLfBJlB6T2eOsET4tlfcLs7oXR7kCyt1xc